fix(core): cross-stack reference error doesn't include violation (#23987)

When users are using cross-stack references that are not allowed, we just tell them the stacks that are involved in the reference, but not the reference itself. For example:

```
Stack "ExampleStack" cannot consume a cross reference from stack
"cross-region-stack-1111111111:us-east-2". Cross stack references are
only supported for stacks deployed to the same environment or between
nested stacks and their parent stack.
```

This makes it very hard to debug what's going on, and why the reference is there in the first place.

Render the reference as well so that it's easier to figure out why this is happening.

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: rix0rrr

Diff for: packages/@aws-cdk/core/lib/private/refs.ts

@@ -61,15 +61,15 @@ function resolveValue(consumer: Stack, reference: CfnReference): IResolvable {
   // unsupported: stacks are not in the same account
   if (producerAccount !== consumerAccount) {
     throw new Error(
-      `Stack "${consumer.node.path}" cannot consume a cross reference from stack "${producer.node.path}". ` +
+      `Stack "${consumer.node.path}" cannot reference ${renderReference(reference)} in stack "${producer.node.path}". ` +
       'Cross stack references are only supported for stacks deployed to the same account or between nested stacks and their parent stack');
   }
 
 
   // Stacks are in the same account, but different regions
   if (producerRegion !== consumerRegion && !consumer._crossRegionReferences) {
     throw new Error(
-      `Stack "${consumer.node.path}" cannot consume a cross reference from stack "${producer.node.path}". ` +
+      `Stack "${consumer.node.path}" cannot reference ${renderReference(reference)} in stack "${producer.node.path}". ` +
       'Cross stack references are only supported for stacks deployed to the same environment or between nested stacks and their parent stack. ' +
       'Set crossRegionReferences=true to enable cross region references');
   }
@@ -113,7 +113,7 @@ function resolveValue(consumer: Stack, reference: CfnReference): IResolvable {
   if (producerRegion !== consumerRegion && consumer._crossRegionReferences) {
     if (producerRegion === cxapi.UNKNOWN_REGION || consumerRegion === cxapi.UNKNOWN_REGION) {
       throw new Error(
-        `Stack "${consumer.node.path}" cannot consume a cross reference from stack "${producer.node.path}". ` +
+        `Stack "${consumer.node.path}" cannot reference ${renderReference(reference)} in stack "${producer.node.path}". ` +
         'Cross stack/region references are only supported for stacks with an explicit region defined. ');
     }
     consumer.addDependency(producer,
@@ -133,6 +133,13 @@ function resolveValue(consumer: Stack, reference: CfnReference): IResolvable {
   return createImportValue(reference);
 }
 
+/**
+ * Return a human readable version of this reference
+ */
+function renderReference(ref: CfnReference) {
+  return `{${ref.target.node.path}[${ref.displayName}]}`;
+}
+
 /**
  * Finds all the CloudFormation references in a construct tree.
  */

Diff for: packages/@aws-cdk/core/test/stack.test.ts

@@ -1698,7 +1698,7 @@ describe('stack', () => {
 
     expect(() => {
       app.synth();
-    }).toThrow(/Stack "Stack2" cannot consume a cross reference from stack "Stack1"/);
+    }).toThrow(/Stack "Stack2" cannot reference [^ ]+ in stack "Stack1"/);
   });
 
   test('urlSuffix does not imply a stack dependency', () => {